Process and product utilizing tobacco stems



United States Patent 3,043,723 PROCESS AND PRDDUCT UTILIZING TOBACCO STEMS Desmond Cleverdon, Ramsey, England, assignor to General Cigar Co., Inc., New York, N .Y., a corporation of New York No Drawing. Filed Sept. 17, 1959, Ser. No. 840,506 17 Claims. (Cl. 131--17) This invention relates to the conversion of tobacco materials to products suitable for smoking and more particularly to tobacco products formed of comminuted tobacco and a binding agent derived from tobacco stems.

In the maufacture of cigarettes certain tobacco materials are normally rejected. These rejects comprise: small particles broken from the tobacco leaf during processing, usually called shorts; small particles of cut tobacco vein and rib usually called winnowings; and the midrib or stem of the tobacco leaf, notably Burley tobacco stem, which because of its undesirable smoking qualities is deliberately discarded.

Many processes have been proposed for the conversion of such rejected tobacco materials into tobacco sheets suitable for use in the manufacture of cigarettes and cigars. However, no prior process has been specifically directed to the important commercial problem of using tobacco rejects including a substantial proportion of tobacco stems in making a tobacco sheet having smoking qualities superior to those of the composite rejects prior to conversion into sheet form.

A primary object of this invention is to utilize tobacco stems along with other tobacco materials to produce sheets or other coherent forms of tobacco of good smoking qualities for incorporation in cigarettes, cigars, cigarillos and pipe tobacco.

Another important object is to process tobacco stem to remove constituents deleterious to smoke taste and to convert the residual stem material to a homogenized pulp particularly well suited for use as the binding agent in making tobacco sheets and like coherent bodies with additional tobacco material in a comminuted state.

These and other objects and advantages of the invention will be apparent from the description which follows.

In accordance with this invention, a quantity of tobacco stems is subjected to aqueous extraction and homogenization to provide a pulp of cohesive properties to which a larger quantity (on a dry weight basis) of finely Patented July 10, 1962 ice to the smoking qualities of the final product is inordinately long in such case. Hence, it is advantageous to shorten the extraction time by working with hot water. Again, while the extraction vessel may be open to the atmosphere, it is desirable to use a scalable vessel suitable for operation at reduced and increased pressures. In

fact, operation first at reduced pressure and ultimately at elevated pressure has been found to give very desirable extraction.

After the tobacco stems have been properly extracted,

i.e., have lost at least by weight (dry basis), the

hammer mill or a disintegrator with a high-speed rotor divided tobacco material is added to yield a mixture that c is readily convertible to sheets and other coherent forms of tobacco by konwn techniques such as applying a layer of the mixture on a supporting surface and drying the layer to a removable film or sheet.

The processing of tobacco stems pursuant to this invention involves two essential'steps: aqueous extraction to eliminate a substantial portion of the extractible components including undesirable alkaloids, such as nicotirie and nornicotine, and ash-producing salts, followed by homogenization of the residual stem material to yield a smooth pulp with cohesive properties.

The aqueous extraction of tobacco stems, which may be aided by variations in temperature and pressure, is carried on generally for a sufiicient period to remove extractibles totaling from about 20% to 60% by weight (dry basis) of the original stems. To hasten extraction, the tobacco stems are usually cut to pieces of about A to /2 inch in length. The cut stems are then placed in an extraction apparatus, e.g., a wire-mesh basket that fits in vessel to which water is charged. While extraction at atmospheric conditions is possible simply by steeping the comminuted stems in water, the time required to achieve the desired elimination of components deleterious within a stator and then subjecting the wet-ground stem material in aqueous suspension to further intensive shearing in'a very high-shear device, preferably a valve-type homogenizer. Microscopic examination and centrifuging tests have revealed that on a comparative basis the most prominent result of the wet grinding operation is the reduction in size of the fibrovascular bundle of the residual stem to fibrils of a length largely in the range of about 0.02 to 0.06 inch, whereas the most outstanding result of the intensive shearing operation is the large increase in the hydration or Water retention of the fibrils. It will be understood that size reduction and hydration of the residual stem material occur concomitantly in both operations but that size reduction seems more characteristic of the wet grinding operation while hydration appears more characteristic of the intensive shearing operation. In fact, the unusually high hydration of the homogenized pulp attainedwith a valve-type homogenizer is a noteworthy feature of this invention As previously mentioned, the. homogenized pulp prepared from extracted tobacco stems is capable of functioning as binding agent for a quantity of finely divided tobacco material greater than the original quantity (on a dry weight basis) of tobacco stems. Tobacco sheets of adequate tensile strength and good smoking qualities are generally obtained by adding from 2 to 4 parts by dry weight of powdered'tobacco to each part by dry weight of the solids in the homogenized stem pulse. A ratio of about 3:1 dry Weights of powdered tobacco to stem pulp is often preferred. In the upper half of that proportioning range, it is often advisable to enhance product tensile strength by adding a minor portion, usually less than 40% by weight, of the powdered tobacco to the residual stem material at the start or before the completion of the homogenization step. The powdered tobacco which is added as such to the homogenized stem pulp is obtained by dry-grinding shorts, winnowings and like tobacco material. Usually, it is advantageous to reduce the drytobacco to particles of which more than 99% by weight pass through a IOO-mesh screen and more than 25% by weight pass through a ZOO-mesh screen. US. Patent 2,897,103, granted July 28, 1959, to A. M. Gottscho, discloses that tobacco sheets of notably high tensile strength areobtained when the amount of tobacco particles passing though a ZOO-mesh screen is increased to more than 86% and preferably more than of the total weight of the powdered tobacco.

As known in the tobacco art, humectants and plasticizers such as glycerol, sorbitol and various glycols are used, inqtobacco smoking products to avoid excessive drying and embrittlement of the tobacco prior to smoking. Humectants and plasticizers are desirably incorporated in the products of this invention at any point in the process after the tobacco stems have been extracted. Hume'ctants and plasticizers in an amount usually not exceeding about by weightand frequently not exceeding about 6% by weight of the dry-ground tobacco are-conveniently added to the homogenized stem pulp when the powdered tobacco is also combined therewith. 'Humectants and plasticizers may be even added to the final product of the invention by applying such materials, usuallyinaquous solution, as a coating or spray on the final product.

' The composite of homogenized stern pulp and dryground tobacco may be converted to a continuous tobacco sheet on a stainless steel conveyor belt equipped with a film applicator such as a reverse roll coater and with drying hoods, all as shown in U.S. Patent 2,747,583. In

' makingtobacco sheets pursuant to this invention, it has been found particularly advantageous to heat the film -or coating applied on the top side of the stainless steel beltby condensing steam on the bottom side. Such technique is illustrated in U.S. Patent 2,155,453. In this way, a very high dryingspeed is attained without impairment of-the final product.

In most instances, the layer of aqueous binding agent and powdered tobacco applied on the conveyor belt is dried to an adherent film that is more readily removable from the belt after reordering, i.e., conditioning with moisture. U.S. Patent 2,747,583 demonstrates reordering of the adherent film with a fine water mist from a spray nozzle whichmay desirably be enclosed by a humidification chamber as illustrated in U.S. Patent 2,867,220. Alternatively, a spongy roller, maintained continuously wet with water, may be disposed in rotating contact with the conveyor belt so that .the dry tobacco -film is moistened as it passes under the roller. As previously indicated, humectants and plasticizers like glycerol may be admixed Withthe water used in reordering the tobacco film.

Thereordered tobacco film is then removed or peeled from the conveyor belt and wound up as a roll of continuous tobacco sheet as shown in U.S. Patent 2,747,583. Often, .a doctor blade is used to facilitate parting of the tobacco sheet from the surface of the belt. Where the tobacco sheet is ultimately shredded for use in the manufacture of cigarettes or pipe tobacco, the sheet may be v tobacco leaves going into the cigarettes or pipe tobacco.

As already indicated, there is considerable advantage in the aqueous extraction of comminuted tobacco stems,

if the operation is started at reduced'pressure and finally completed'at elevated pressure. Specifically, it is well to place the comminuted stems in a sealed extraction vesseland to draw a vacuum of say inches of mercury for a period of at least 10 minutes before Water is admitted into the vessel. In this way, air will diffuse from the mass of stem particles, making it more receptive to water penetration and extraction. Hot Water is then introduced into the extraction vessel, while maintaining the vacuum, to submerge the stem particles. On the order of -6 pounds of water are usuallyrequired for each-pound of tobacco stems. The contents of the extraction vessel are kept boiling under vacuum for a period of about minutes when the liquor is drained off and discharged. A fresh charge of hot water is injected into the extraction vessel and brought to boiling for an additional period of 30 minutes. The cycle of peated .a few more times usually not more than two States: gallons.

is left in the extraction vessel and the pressure is raised to say about 25 p.s.i.g. (pounds per square inch gauge). Again, the contents are boiled at the elevated pressure for another period of about 30minutes and then the liquor is drained off. The last pressurized cooking period seems beneficial not only in enhancing the softening and swelling of the extracted stem material but also in sterilizing the residual stem material so that it can be stored for periods of a few days without spoilage from bacterial attack.

While a series of batch Water extractions as just described is effectively carried out in fairly simple equipment, continuous extraction may alternatively be performed in a vessel provided with means to maintain a substantially continuous flow of fresh water into the vessel. with a commensurate outflow of liquor. Preferably, a circulating pump would be used in such case to effect a rapid circulation of liquor through the extraction vessel, In short, continuous extraction may be achieved by adaptation of the continuous blow-down procedure used in conventional boiler practice.

The residual stem material, drained of extraction liquor, undergoes size reduction in the presence of added water in a wet hammer mill which maybe supplemented by an ultrasonic disintegrator wherein a high speed jet of the aqueous suspension of residual stem materials impinged on a thin steel reed in a tuned cavity. During size reduction, the aqueous suspension desirably has a consistency of about 2.5% to 3.0% by Weight (dry basis) of stem material.

Hydration of the wet-ground stem material is readily attained in a valve-type homogenizer for which the aqueous suspension is advisably adjusted With added Water to a lower consistency of say between 1.7% and 2.3% by Weight (dry basis) of stem material. Generally, the valve-type vhomogenizer is operated at a pressure of the order of 2000 p.s.i.g. or higher; a pressure of about 5000 p.s.i.g. is often preferred, Again, warming the aqueous suspension to a temperature in the range of about to 250 F. favors hydration of the residual stem material during passage through the valve-type homogenizer. As known, in a valve-type homogenizer the aqueous suspension at the chosen elevated pressure enters a controlledmicroscopic clearance between the homogenizing valve and valve seat. At this point the high pressure is instantaneously changed to high velocity so that the material passing through the clearance at extremely high velocity is subjected to high shear, extreme and intense turbulence, cavitation and impact. The impact action occurs as the material leaves the clearance and impinges on the impact ring surrounding the valve clearance.

For a better understanding of the invention and its scope, illustrative embodiments are presented hereinbelow in detail. Liquid quantities aregiven in-terms of United EXAMPLE 1 A 220-pound batch of Barley stems, cut to pieces less than /2 inch long, was placed in a meshed stainless steel basket which fitted into a 400 gallon jacketed vessel provided with recirculating pump, blow-down pump, vacuum pump and hot water (140 F.) feed line. Without adding water to the stems, which had about 10% moisture content, a vacuum of 25 inches of mercury was drawn. After 10 minutes, 300 gallons of hot Water were added. The vacuum was continued and the steam valve to the jacket of the vessel was opened to give 10 p.s.i.g. steam pressure initially and thereafter controlled to maintain the liquor in the vessel at a temperature of 140 to F.

The recirculation pump was started. After 10 minutes of liquor recirculation, the blow-down pump was started up and hot water was added to maintain the original liquor level in the extraction vessel. Blow-down under vacuum with continuous hot water addition to hold the water level was carried out for an hour. The supply of hot water was then shut ofi as well as the vacuum pump and the blow-down pump. The vacuum was re leased and the steam pressure in the jacket adjusted to 50 p.s.i.g. Whenthe pressure in the vessel reached 23 p.s.i.g., the steam pressure in the jacket was lowered and thereafter adjusted to maintain a pressure of from 23 to 25 p.s.i.g. in the vessel. Pressurized cooking was continued for 30 minutes.

Cold water was next admitted to the vessel and when the gauge pressure had dropped to zero, the recirculation flow was diverted to the drain. Cold water was kept flowing through the vessel until the effluent was lukewarm. The cold Water valve was then shut and compressed air admitted to the vessel to facilitate draining of the residual stem material. In all, 49% of the dry weight of the original stems was eliminated by extraction.

The drained stem material was fed into the hopper of a screw conveyor and thence, with continual addition of water, into a series of wet hammer mills. Three hammer mills were used of successively decreasing screen size from inch to 0.006 inch.

The aqueous suspension from the wet hammer mills Was next passed 6 times through a valve-type homogenizer at a pressure of 5000 p.s.i.g. Water was added to the homogenized stem pulp to arrive at a final consistency of from 2.0% to 2.1% by weight of dry solids.

Glycerol in the amount of 15.3 pounds was admixed with the pulp. Tobacco flour, dry-ground so that 100% by weight of it passed a 100-mesh sieve and more than 30% passed a ZOO-mesh sieve, was blended in with the homogenized stem pulp to the extent of 306 pounds. The tobacco rejects which were ground to provide the tobacco flour were obtained partly from the leaf drying plant and partly from the cigarette factory and comprised both air-cured and flue-cured tobaccos. The mixture of homogenized pulp and tobacco flour was de-aired by spraying into a vacuum chamber, and then applied by means of a gated hopper as a wet coating of 0.045 inch in thickness, on a conveyor belt of stainless steel. The coating was dried with the aid of steam condensed on the bottom side of the belt, reordered and removed from the stainless steel belt with the aid of a doctor blade.

The tobacco sheet thus produced, between 0.008 and 0.010 inch in thickness, was continuously slit and cut into small-rectangular pieces which were subsequently blended with leaf tobacco and converted into cigarettes by the conventional manufacturing technique. Cigarettes made with a tobacco blend containing 12% by weight of the shredded tobacco sheet were adjudged by smoking experts to have good smoking qualities, some experts even indicating a preference for these cigarettes over cigarettes made with the same tobacco blend but containing none of the shredded tobacco sheet.

EXAMPLE 2 A 9.5 pound batch of Burley stems with 13% moisture content was chopped to pieces approximately inch in length. The chopped stems were placed in a vessel with a sealable lid having connections to a vacuum pump, a water line, a dip tube extending to the bottom of the vessel and having a strainer on its end, and a pressurized gas line. A gas ring was used under the vessel to heat the contents. A vacuum of 25 inches of mercury was applied for one hour. Then 5 gallons of Water were added and the whole charge boiled under vacuum for half an hour. Heating was discontinued, the vacuum line was closed and a pressure of 5 to p.s.i.g. was applied by introducing oxygen-free nitrogen into the vesselfor the purpose of ejecting the liquor through the dip tube. The liquor, after analysis, was discarded. Vacuum was reapplied, rnore water added, and the charge boiled again under vacuum for thirty minutes. As shown in Table I, five such extractions were made, except that on the fifth occasion, after boiling under vacuum for half an hour,

6 the charge was pressure cooked at 248 to 259 F. and 14 to 20 p.s.i.g. for one hour.

The electrical conductivity is"expressed as the ratio of that of the liquor to that of a decinormal potassium chloride solution at 77F.

The residual stem material (extraction loss approximately 50% by dry weight of original stems) was fed with addition of just sufi'icient water to maintain flow through a wet hammer mill fitted with a inch screen. It was then repassed through the mill after the principal screen had been changed to 0.027 inch.

At this stage, an aliquot of the aqueous suspension was taken and its consistency determined. Water was added to bring the consistency to 2% by weight of dry solids and a water retention value was determined under the following conditions.

A centrifuge with four 10 milliliter cups was employed to subject 9 to 10 grams of the suspension at a temperature of 68 to 72 F. to a relative centrifugal force of 716 g (g being acceleration due to gravity) for 10 minutes. The centrifuge used had an effective radius of 7.1 centimeters and 3,000 revolutions per minute were required to produce the desired centrifugal force. As the centrifuge had four cups it was convenient to carry out four determinations at the same time on portions of the suspension; The centrifuge tubes were weighed before and after adding the suspension, and were reweighed after centrifugation and pouring off the supernatant liquor. The water retention value, R, was calculated from the following equation:

. M -lll where The R values obtained were 11.0, 12.1, 11.6 and 11.7,

with a mean value of 11.6.

The main portion of the aqueous suspension was then fed with added Water through a gear pump and an ultrasonic disintegrator, and given sev en complete passes through a valve-type homogenizer operating at 2000 p.s.i.g. The homogenized stem pulp thus produced amounted to pounds containing 2.17% by weight of dry solids.

The pulp from the valve-type homogenizer was subjected to the Water retention value test and the following R values were obtained: 25.4, 24.8, 25.0, 24.5, with a mean value of 24.9. The increase of water retention value between the wet hammer milling stage and the homogenization stage (11.6 to 24.9) is quite striking.

To the homogenized stem pulp was added tobacco flour made from 5.1 pounds of shorts and 3.4 pounds of winnowings. All of this tobacco flour had been passed through a IOO-mesh screen. After admixing 0.25 pound of glycerol, the entire mixture was subjected tovacuum for half an hour in order to deaerate it.

A portion of the deaerated mixture was cast upon a stainless steel belt traveling at 20 feet per minute and heated from the underside'iby steam at a gauge pressure of approximately half an inch of water. Casting was achieved by means at a gated hopper set with its forward blade 0.035 inch from the surface of the belt. Difiiculty was encountered in getting an even coating of the mixture on the belt and, therefore, water was added to the remainder of the mixture to give it a consistency of 1.75% by weight. This mixture of'lower consistency cast evenly as a wet coating of 0.035 inch in thickness, was dried and then rehumidified by means of a spongy roller receiving a constant drip of water rolling lightly over the surface of the tobacco sheet. A doctor blade of a laminated plastic material was used to remove the tobacco sheet continuously from the stainless metal belt.

This sheet, between 0.006 and 0.007 inch in thickness, was-cutinto small pieces and blended with leaf tobacco, the latter amounting to 8 8% by weight of the blend. The blend was cut on a conventional cutting machine and converted into cigarettes. These cigarettes were judged to be of pleasing smoke taste by a panel .of smoking experts familiar with cigarettes made solely with the same leaf tobacco.

EXAMPLE 3 A '10,pound batch of Burley stems with a moisture content, cut to pieces about 2 inches in length, was placed in the extraction vessel of Example 2. A vacuum of inches of mercury was applied for one hour. The stem was given only one aqueous extraction of 4.5 hours with boiling under vacuum; toward the end of the extraction the vacuum had improved to '27 inches of mercury and the charge was boiling at 117 F. After ejection of the liquor, the residual stem material was wet hammer-milled, passed through an ultrasonic disintegrator and homogenized in the manner described in Example 2. The homogenized stem pulp thus produced amounted to 240 pounds at a consistency 2.1% by weight of dry solids. As in Example 2, 3 parts v(dry weight) of tobacco flour were added to 1 apart (dry weight) of homogenized stem pulp. Glycerol was also added to the extent of 5% by weight of the tobacco flour. In the manner of Example 2, the mixture was cast as a wet coating 0.040 inch thick and dried to a tobacco sheet about 0.006 inch thick.

Cigarettes made after the manner of Example 2 were judged to be of good smoke taste but to be somewhat stronger in flavor than the cigarette of Example 2.

EXAMPLE 4 An 8:5 pound batch of Burley stems with 14.2% moisture content, cut to pieces about 2 inches in length, was placed in the extraction vessel of Example 2. Four vacuum extractions were carried out, the last being finished on by a pressure cook for one hour at 20 p.s.i.g. and 259 P. On this occasion the liquor was analyzed to estimate totalalkaloids; the progressive dealkaloidization of the stem may be seen from TableI'I. The starting stem contained, on a dry-weight basis, 1.0% of total alkaloids, expressed-as nicotine, that is 0.073 pound.

1 The electrical conductivity is expressed as the ratio of that of the liquor to that of a decinormal potassium chloride solution at 77 F.

In accordance with the procedure of Example 2, the residual stem material 'was converted into 224pounds of homogenized pulp with a consistency of 2.15% by Weight cf-dry solids, representing-a yield of 66% by weight of the Burley stems on-a dry solids basis. Tobacco flour and glycerol were added to the homogenized stem pulp and the mixture was converted into a tobacco sheet, all as described in Example 2.

Cigarettes in which the tobacco blend contained 12% by weight of the sheet in shredded form were found to be mild and pleasant and were preferred by some smokers to similar cigarettes containing none of the sheet.

EXAMPLE 5 A 10 pound batch of Burley stems with 11% moisture content was extracted by following the procedure of Exv ample 2. Approximately 50% of the dry weight of the original stems was removed by extraction.

To the Wet residual stem material were added 3.2 pounds of the fines obtained in rolling Virginia tobacco stems and 1.8 pounds of winnowings flaked between diiferential calendar rolls so that these two forms of tobacco scrap also entered the wet hammer mills. The resulting aqueous suspension with added water was passed 3 times through a wet hammer mill, t-wice through an ultrasonic disintegrator and 6 times through a valve-type homogenizer at a pressure of 5000 p.s.i.g.

The homogenized pulp thus prepared was admixed with 10 pounds of the tobacco flour used in Example 1. Accordingly, only one-third of the total tobacco rejects ad mixed with the extracted Burley stems was homogenized therewith. After adding 0.75 pound of glycerol, the mixture was cast as .a wet coating of 0.050 inch thickness on a conveyor belt of stainless steel and dried to a tobacco sheet of 0.009 to 0.010 inch thickness by condensing steam on the opposite side of the belt.

Cigarettes made by blending 12% by weight of the resulting tobacco sheet with leaf tobacco were rated by a panel of smoking experts indistinguishable from the cigarettes of Example 1.

EXAMPLE 6 The midribs of Nigerian flue-cured tobacco were subjected to four vacuum extractions of thirty minutes each, the last extraction being finished ofi by a pressure cook for one hour at 30 p.s.i.g. Data from the four extractions are given in Table III and are based on 10 pounds of stems with 1 8.2% moisture content.

Table III Liquor Analysis Added Elected Extraction No. Water, Liquor,

gals. gals. pH Dissolved Conduc- Solids lbs. tivity 1 to that ot a decinormal potassium chloride solution at 77 Itwas observed that the residual stem material had softened more than that from Burley stems extracted under comparable conditions. Consequently, this residual stem material was passed much more easily through the wet hammer mills, the ultrasonic disintegrator and the valve-type homogenizer operating at 2000 p.s.i.g. After six passes through the valve-type homogenizer, the pulp had a water retention value (see Example 2) of 21 and after twelve passes the water retention value was 30.

The homogenized stem pulp thus produced amounted to 152.5 pounds containing 2.5% by weight of dry solids. To 46 pounds of this homogenized pulp were added 3.4 pounds of Nigerian flue-cured whole leaf tobacco with 11.2% moisture content in powdered form and 0.15 pound of glycerol. The mix-ture was applied on a stainless steel belt as a wet coating of 0.045 inch thickness and dried with the aid of steam condensed on the opposite side of the belt to a tobacco sheet of about 0.009 inch thickness. The tobacco sheet had a golden color and pleasing smoke taste.

Under substantially the same conditions, the stems of Nigerian air-cured tobacco and powdered Nigerian aircured tobacco gave similar desirable results.

EXAMPLE 7 The extraction and homogenization procedures of Example 6 were carried out with pounds of stems of Jamaican bulk-sweated, flue-cured tobacco with 18 moisture content and yielded 117 pounds of homogenized Y the other case it was Jamaican bulk-sweated, air-cured whole leaf tobacco in pulverized form.

Each of the two mixtures was spread on a stainless steel belt as a wet coating of 0.050 to 0.055 inch thickness and dried to a tobacco sheet of 0.009 to 0.010 inch thickness. Both tobacco sheets were found satisfactory in the manufacture of cigarettes.

EXAMPLE 8 A 9 pound batch of stems from Connecticut shadegrown tobacco with moisture content was chopped into pieces of approximately /2 inch in length. These stem pieces were placed in a vessel as described in Example 2. The vessel was sealed and a vacuum of 25 inches of mercury was drawn and held for 30 minutes. Seven gallons of hot water were added to the stems in the vessel and the mixture was boiled under vacuum for half an hour. The liquor was drawn off and replaced with an equal quantity of fresh hot water. The vacuum boil was repeated for an additional half hour. At the end of this period, the vacuum was released, the vessel rescaled and heating continued until a pressure of p.s.i.g. was attained. The batch was held at this pressure for one hour, after which the liquor was drawn oif. The dry weight of the extracted stems was about 60% of the initial dry weight.

These extracted stems were suspended in sufficient water to bring the consistency of the resulting slurry to approximately 2% by weight of dry solids. The aqueous suspension was then passed through a wet hammer mill three successive times, each time using a progressively smaller screen opening varying from inch to 0.016 inch. Thence, the aqueous suspension was passed six times through a valve-type homogenizer operating at a pressure of 5000 p.s.i.g. The consistency of the homogenized stem pulp was measured and found to be 2.2% by weight of dry solids. The homogenized stem pulp had a water retention value of about 24.

To 200 pounds of the binding agent pulp thus prepared who-11y from tobacco stems was added a tobacco flour blend consisting of 4 pounds of ground tobacco dust obtained from cigar filler drying and blending operations, 6 pounds of ground filler tobacco obtained as small cuttings from cigar-making machines, and 3 pounds of ground tobacco dust collected from cigar filler threshing operations. These tobacco flours, ground to pass completely through a LOO-mesh screen, in themselves consisted of blends of typical cigar filler tobaccos from Pennsylvania, Maryland, Havana and Puerto Rico.

After adding with stirring 1 pound of triethylene glycol,- the mixture was deaerated for one hour under vacuum. The mixture was then continuously cast on a stainless belt, dried, rehumidified and doctored from the moving belt, all as described in Example 2. As the tobacco sheet came oif the belt, it was cut into pieces approximately 3 inches square and collected. This material was passed 10 through a tobacco cutter and mixed with cut cigar filler leaf tobacco so that the blend contained 3% by weight of tobacco sheet. This blend Wasusedaas filler in the manufacture of cigars having a pleasing smoke taste.

Throughout this specification, dry weights have been determined by drying solids to constant Weight in a dryer maintained at a temperature of 212 F.

It is also well to note that the homogenized stem pulp prepared pursuant to this invention has residual fiber frag ments which are readily seen in a low-power microscope or large field inspection enlarger. While long fiber length has the advantages of increasing both tensile strength and fold resistance of the ultimate tobacco sheet, difliculties from plugging or blocking are encountered in the valvetype homogenizer when the pulp contains long fiber fragments. Also, long fiber length leads to further difficulties when the final mixture is to be spread smoothly and evenly on a supporting surface. For such reasons, residual fiber fragments will in most instances not exceed 0.3 inch in length. The very high water retention values obtained by passing the aqueous suspension of extracted stem material through a valve-type homogenizer appears attributable at least in part to the existence of fiber fragments in a highly swollen condition in the homogenized pulp. In turn, these swollen fiber fragments present in the aqueous binding agent of this invention contribute to the tensile strength of the sheet or like coherent form of tobacco ultimately produced. Experience has shown that in gen eral tobacco sheets are readily made when the aqueous binding agent, i.e., the homogenized stem pulp, has a water retention value of at least about 20 measured by the test described in Example 2. Prolonged homogenization increases the water retention value of the pulp but the consequent greater power consumption for water retention values exceeding 35 is difiicult to justify economically. In the usual operation, a water retention value of the order of 25 is set as the manufacturing standard.

Many variations and modifications of the invention hereinabove disclosed will be visualized by those skilled in the art without departing from its spirit and scope. For instance, comminuted stems, after being deaerated under vacuum, may be submerged with water and directly cooked at an elevated pressure for a period that will achieve the desired extraction, i.e., at least about 20% by weight of the dry stems, or for a short period that will be supplemented, after replacing the liquor with fresh water, by additional cooking periods carried out at elevated pressure and/ or reduced pressure. Likewise, while US. Patent 2,747,583 shows the drying hoods operating with heated air blown against the coated conveyor belt, where steam is condensed on the bottom side of the belt to dry the coating on the opposite side, the drying hoods operate satisfactorily with blowers drawing ambient air and the moisture evaporated from the coating up through the hoods. Accordingly, the claims should not be interpreted in any restrictive sense other than that imposed by the limitations recited within the claims.

What is claimed is:

1. The improved process of converting tobacco into a coherent form adapted for smoking, which comprises extracting a quantity of tobacco stems with water to eliminate extractible components to an extent of at least about 20% by dry weight of said stems, wet-grinding the residual stem material, subjecting the resulting aqueous suspension of said stem material to pressurization and intensive shearing homogenization to yield a highly hydrated pulp having a water retention value of at least about 20, combining a quantity of dry-ground tobacco with said pulp, said quantity of dry-ground tobaccobeing greater on a dry Weight basis than the dry solids in said pulp, and drying the combined pulp and dryground tobacco into said coherent form.

2. A tobacco smoking product comprising a major portion by dry weight of dry-ground tobacco and a minor portion by dry weight of tobacco-derived binding agent 11 holding theparticles of-said dry-ground tobacco together as :said smoking iproduct, said binding agent consisting essentially ot an aqueous-extracted tobacco stem residue amounting to not more than 80% by dry weight of the original. tobacco stems subjectedto aqueous extraction,

said stem residue having been pressurized and converted by intensive shearing homogenization to a highly hydrated pulp having a water retention value of at least about 20.

3. In a tobacco smoking product made of finely difunctioning to hold the particles of saidfinely divided tobacco together as said smoking product.

4. The product of claim 3 wherein the original tobacco stems are those of flue-cured tobacco.

5. The product of claim 3 wherein the original tobacco stems are thoseof Burleytobacco.

'6. In the manufacture of a coherent tobacco smoking productvfrom finely dividedtobacco and an aqueous binding agent for said tobacco, the improvement of preparing said aqueous binding agent from tobacco stems which comprises subjecting said stems to aqueous extraction to remove therefrom extractible components to the extent of at least about 20% by dry weight of said stems, and effecting pressurization and intensive shearing homogenization of the residual stem material in the presence of water to yield ahighly hydrated pulp of cohesive properties as said aqueous binding agent, said pulp having a aqueous extraction is carried out with boiling water at subatmospheric pressure.

10. The process of claim 1 wherein the dry-ground tobacco is in the range of 2 to 4 parts by dry weight for vided tobacco and a binding agent, the improvement of v 12 each .part by weight of the .dry .solids in the highly hydrated pulp.

11. The process of claim .1 wherein 'Burleytobacco stems in comminutedfform are deaerated under vacuum prior to extracting said s'temswith water.

12. The process of claim 1 wherein a minor part of the finely divided tobacco is-admixed with the residual stem material prior to homogenization.

13. The process of claim 1 wherein the aqueous suspension of stem material is at a temperature in the range of about 140 to 250 F. during homogenization.

14. The product of claim 2 wherein the major portion of dry-ground tobacco is in the range of 2 to 4 parts by dry weight for each part by weight of the dry solids in the tobacco-derived binding agent.

15. An improved aqueous binding agent for binding tobacco particles together in a continuous and coherent form, which consists of a homogenized aqueous pulp of residual stem material obtained by water extraction of tobacco stems, said residual stem material amounting on a dry basis to from 40% to 80% by weight of said tobacco stems, said homogenized aqueous pulp having a water retention value of at least about 20.

16. The binding agent of claim 15 wherein the homogenized aqueous pulp has a consistency of at least about 2% by weight of dry solids.

17. The binding agent of claim 16 wherein the residual stern material amounts-on a dry basis on the order of by weight of the tobacco stems, and the homogenized aqueous pulp'has a water retention value on the order of 25.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,043,723 July 10, 1962 Desmond Cleverdon It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 13, for "aquous" read aqueous line 71, for "discharged read discarded column 4, line 27, for "materials" read material is column 9, line 71, after "stainless" insert steel column 12, line 7, for "finely divided" read dry-ground line 22, after "pulp" insert having been subjected to pressurization and intensive shearing homogenization and same column 12, list of references cited, and the following:

FOREIGN PATENTS 16,550 Great Britain A.D. 1893 Signed and sealed this 1st day of January 1963.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

1. THE IMPROVED PROCESS OF CONVERTING TOBACCO INTO A COHERENT FORM ADAPTED FOR SMOKING, WHICH COMPRISES EXTRACTING A QUANTITY OF TOBACCO STEMS WITH WATER TO ELIMINATE EXTRACTIBLE COMPONENTS TOAN EXTENT OF AT LEAST ABOUT 20% BY DRY WEIGHT OF SAID STEMS, WET-GRINDING THE RESIDUAL STEM MATERIAL, SUBJECTING THE RESULTING AQUEOUS SUSPENSION OF SAID STEM MATERIAL TO PRESSURIZATION AND INTENSIVE SHEARING HOMOGENIZATION TO YIELD A HIGHLY HYDRATED PULP HAVING A WATER RETENTION VALUE OF AT LEAST ABOUT 20, COMBINING A QUANTITY OF DRY-GROUND TOBACCO WITH SAID PULP, SAID QUANTITY OF DRY-GROUND TOBACCO BEING GREATER ON A DRY WEIGHT BASIS THAN THE DRY SOLIDS IN SAID PULP, AND DRYING THE COMBINED PULP AND DRYGROUND TOBACCO INTO SAID COHERENT FORM. 